Understanding and coordinating the complex, interdependent activities of early innate response elements with subsequent powerful adaptive immune responses are vital for developing more successful approaches for the immunotherapy of cancer. In this regard, it is important to understand the unique dynamics that occur in the tumor micro-environment such that events beneficial to the tumor are subverted while events beneficial to the host are enhanced. In this context CD40, a TNF superfamily receptor serves as a potent trigger for dendritic cells which provide a key interface between innate and adaptive responses. The potency of dendritic cell stimulation by agonist CD40 antibodies is enhanced when used in conjunction with IL-2 and the combination of agonist anti-CD40 plus IL-2 shows enhanced antitumor activity against metastatic kidney cancer in mice. Because CD40 is present on various hematopoietic-derived cells, endothelial cells, and some tumors themselves, we have also performed studies to definitively determine if the antitumor effects of CD40 stimulation and IL-2 were primarily mediated by CD40+ hematopoietic-derived cells. Bone marrow chimeras were created by reconstituting lethally irradiated CD40+/+ recipients with bone marrow from CD40-/- or CD40+/+ mice. Chimeric mice were then implanted orthotopically with renal cancer cells followed by treatment with anti-CD40 agonist mAb and IL-2. The anti-tumor effects in the CD40-/- BMT chimeras were almost completely abrogated after treatment demonstrating that hematopoietically-derived CD40+ cells are the principal targets for CD40 stimulation in this model. While both spleen and liver revealed reductions in CD8+ T and dendritic cell expansion in the CD40-/- vs. CD40+/+ chimeras after therapy, only the liver exhibited no significant increases in either CD8+ T cells or dendritic cells after treatment. CD40 present on hematopoietic cells are the primary targets for anti-CD40 and IL-2 therapy. The results also suggest that the immunological events in the liver may be more revealing that those in lymphoid organs with regard to critical events related to responses after therapy. In addition, targeted disruption of other events in the tumor microenvironment may ultimately reveal new approaches for combining immunotherapy with other molecularly targeted strategies. In this regard, we have made expression vectors encoding the soluble forms of the VEGF receptors (VEGFRs), Flk-1 and Flt-1, linked to the constant region of human IgG1, and delivered these plasmids to Balb/c mice by highly efficient hydrodynamic injection, this strategy resulted in up to 0.1mg/ml of the appropriate gene products in mouse serum and successfully inhibited angiogenesis in VEGF-containing matrigel. Growth in vivo of a Balb/c mouse renal cancer was also blocked by the same treatment, particularly with soluble Flt-1. The expression of several other proangiogenesis-associated genes, MMP-2 and COX-2 in Renca tumors were also downregulated by soluble Flk-1 gene delivery, suggesting a broader effect of VEGF-neutralization on the overall angiogenic phenotype.